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MergeIntervals.java

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import java.util.ArrayList;

import java.util.Arrays;

import java.util.Comparator;

/**

* Given a collection of intervals, merge all overlapping intervals.

*

* For example,

* Given [1,3],[2,6],[8,10],[15,18],

* return [1,6],[8,10],[15,18].

*/

public class MergeIntervals {

public class IntervalCmp implements Comparator<Interval> {

@Override

public int compare(Interval i1, Interval i2) {

if (i1.start < i2.start) return -1;

if (i1.start == i2.start && i1.end <= i2.end) return -1;

return 1;

}

}

public ArrayList<Interval> merge(ArrayList<Interval> intervals) {

ArrayList<Interval> ret = new ArrayList<Interval>();

if (intervals.size() == 0) return ret;

Interval[] arr = new Interval[intervals.size()];

intervals.toArray(arr);

Arrays.sort(arr, new IntervalCmp());

int start = arr[0].start;

int end = arr[0].end;

for (int i = 0; i < arr.length; i++) {

if (arr[i].start <= end) {

end = Math.max(end, arr[i].end);

} else {

ret.add(new Interval(start, end));

start = arr[i].start;

end = arr[i].end;

}

}

ret.add(new Interval(start, end));

return ret;

}

}